JP5655945B2 - Electric double layer capacitor - Google Patents

Description

The present invention relates to various electronic devices and that used such as vehicle power storage device electric double layer capacitor.

  The electric double layer capacitor includes a capacitor element, a metal case, and a rubber seal. The capacitor element includes a positive electrode in which an electrode layer containing activated carbon is formed on a metal foil, a negative electrode having a configuration similar to that of the positive electrode, and a separator interposed between the positive electrode and the negative electrode. The capacitor element is accommodated in the metal case together with the electrolytic solution, and the rubber sealing member seals the opening of the metal case. And in order to pull out an electrode from a capacitor element, connecting members, such as a lead wire, are joined to each of a positive electrode and a negative electrode, and it is the structure pulled through the said rubber sealing body.

  A quaternary ammonium salt or a quaternary phosphonium salt is used as a solute in the electrolyte of a conventional electric double layer capacitor. These solutes have the property of being chemically active. Therefore, when the electric double layer capacitor using these solutes is repeatedly charged and discharged under severe conditions such as high temperature, the pH of the electrolyte near the negative electrode is biased toward the alkali side, and the electrolyte on the surface of the negative electrode It may creep up and leak from the rubber seal to the outside. Moreover, the lead wire which pulls out an electrode from a rubber sealing body or a negative electrode may be corroded by contacting with the electrolyte which goes up.

  A conventional proposal for such a problem will be described with reference to FIG. FIG. 3 is a schematic view showing a current collector and a rubber seal used in a conventional electric double layer capacitor. A tab terminal 102 as a lead wire is connected to the current collector 101 constituting the negative electrode, and the tab terminal 102 is inserted into a through hole 103 </ b> A provided in the rubber seal 103.

  In such a configuration, a chemical conversion film using a chemical agent having an oxidizing property is formed on the surfaces of the current collector 101 and the tab terminal 102 in order to increase resistance to corrosion due to leakage. Then, butyl rubber is resin vulcanized or peroxide vulcanized on the rubber sealing body 103 having the through-hole 103A so that the hardness of the rubber sealing body 103 is in the range of 60 to 90 (according to a Wallace hardness meter). Such a method has been proposed.

  Thereby, even if a quaternary ammonium salt or a quaternary phosphonium salt is used as the solute of the electrolytic solution, it is possible to suppress the leakage of the electrolytic solution from the rubber sealing body 103 to the outside (for example, Patent Document 1). ).

JP-A-7-122467

The present invention, even if the charge and discharge in severe conditions such as high temperature, gas-electric change and creeping of pH is increased reliability is suppressed is double layer capacitor. Electric double layer capacitor of the present invention, the electrolytic solution, and lactones, see containing a tertiary amine compound represented by the quaternary ammonium salt of the formula contained in the lactone (1), the A tertiary amine compound is contained in an amount of 0.01 wt% to 5 wt% .

C represents a carbon atom, H represents a hydrogen atom, O represents an oxygen atom, and N represents a nitrogen atom.

  With this configuration, it is possible to suppress hydrolysis of the solvent caused by a trace amount of water contained in the electrolytic solution. Thereby, the fluctuation | variation of pH in electrolyte solution is suppressed, and the creeping of the electrolyte solution in the negative electrode vicinity can be suppressed. As a result, liquid leakage can be suppressed in the electric double layer capacitor using such an electrolytic solution.

FIG. 1 is a partially cutaway perspective view of an electric double layer capacitor according to an embodiment of the present invention. FIG. 2 is a schematic diagram of an H-type cell used in an electrolytic solution performance evaluation test in the embodiment of the present invention. FIG. 3 is a schematic diagram showing a negative electrode to which a tab terminal used in a conventional electric double layer capacitor is connected and a rubber sealing member.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as measures for suppressing fluctuations and creeping of pH and improving the reliability of an electric double layer capacitor. The configuration of the present invention is not limited to the following contents.

  FIG. 1 is a cutaway perspective view of an electric double layer capacitor according to an embodiment of the present invention. The electric double layer capacitor includes a capacitor element 1, an electrolyte solution (not shown), a case 6, and a sealing member 7. Capacitor element 1 has a positive electrode 2, a negative electrode 3, and a separator 4 interposed between positive electrode 2 and negative electrode 3. The electrolytic solution is impregnated in the capacitor element 1. The case 6 contains the capacitor element 1 and the electrolytic solution. The sealing member 7 seals the opening of the case 6.

The positive electrode 2 includes a metal current collector 2A and a polarizable electrode layer 2B formed on the surface of the current collector 2A and capable of adsorbing and desorbing anions in the electrolytic solution. The negative electrode 3 has a metal current collector 3A and a polarizable electrode layer 3B formed on the surface of the current collector 3A and capable of adsorbing and desorbing cations in the electrolytic solution. In FIG. 1, the capacitor element 1 is configured by winding the separator 4 between the positive electrode 2 and the negative electrode 3, but may be configured by stacking them. For the separator 4, for example, cellulose paper having a thickness of about 35 μm and a density of 0.45 g / cm ³ or polytetrafluoroethylene non-woven fabric is used.

  A lead wire 5 </ b> A is connected to the surface of the positive electrode 2 as a lead member, and a lead wire 5 </ b> B is connected to the surface of the negative electrode 3. The sealing member 7 is provided with a pair of through holes 7A, and the lead wires 5A and 5B are drawn out through the through holes 7A.

  The sealing member 7 is disposed in the opening of the bottomed cylindrical case 6 with the lead wires 5A and 5B passing through the through hole 7A. Then, drawing is performed from the outer peripheral surface in the vicinity of the opening of the case 6 where the sealing member 7 is located toward the inside of the case 6, and the opening end of the case 6 is subjected to curling. By these processes, the sealing member 7 is crimped and gripped and fixed. Thereby, sealing of the opening part of case 6 is completed and an electric double layer capacitor is completed.

  Next, the positive electrode 2 and the negative electrode 3 will be described in detail. As the current collectors 2A and 3A, for example, a high-purity aluminum foil (containing 99% or more Al) having a thickness of about 15 μm can be used. This aluminum foil is used after its surface is roughened by electrolytic etching in a chlorine-based etching solution. Polarizable electrode layers 2B and 3B are formed on the front and back surfaces of the current collectors 2A and 3A thus roughened. Examples of materials constituting the polarizable electrode layers 2B and 3B include activated carbon, a binder, and a conductive additive.

  The activated carbon is, for example, a phenol resin activated carbon having an average particle size of 5 μm. The binder is, for example, an aqueous solution of carboxymethyl cellulose (CMC). The conductive auxiliary is, for example, acetylene black. These are mixed in a weight ratio of 10: 2: 1 to prepare a mixture. Further, this mixture is kneaded with a kneader to adjust the viscosity within a predetermined range to produce a paste.

  This paste is applied to both surfaces of the current collectors 2A and 3A, and dried in an air atmosphere at 100 ° C. to form polarizable electrode layers 2B and 3B having a thickness of 40 μm to produce an electrode precursor. Thereafter, the electrode precursor is slit to have a predetermined width. Further, the polarizable electrode layers 2B and 3B are partially removed, and the lead wires 5A and 5B are connected to the exposed current collectors 2A and 3A by a method such as needle caulking, respectively. As described above, the positive electrode 2 and the negative electrode 3 are completed.

  As the activated carbon, in addition to the phenol resin-based activated carbon, a carbon material made of coconut shell, wood powder, paper, petroleum coke, petroleum pitch, or the like may be used. There is no particular limitation as long as it is a porous body that absorbs and desorbs ions on its surface.

  The case 6 is formed of a metal such as aluminum, copper, or nickel from the viewpoint of heat dissipation. The type of metal is not particularly limited as long as it is a material that is less likely to react with the electrolytic solution. The case 6 may be a prismatic case or a laminate type.

  Examples of the material of the sealing member 7 include butyl rubber. However, it is not particularly limited as long as it is a rubber material having elasticity.

  Next, the electrolytic solution will be described. The electrolytic solution contains an organic solvent, a solute contained in the organic solvent, and a tertiary amine compound represented by the formula (1).

R ¹ and R ² are a methyl group or an ethyl group, R ³ is a functional group having a hydroxy group bonded to a straight chain and a terminal carbon composed of three or more carbon atoms, C is a carbon atom, H is a hydrogen atom, O represents an oxygen atom, and N represents a nitrogen atom.

  The organic solvent is not particularly limited as long as it is an aprotic solvent capable of ionizing anions and cations constituting the solute. For example, γ-butyrolactone or propylene carbonate can be used as a typical example. In addition, lactones may be γ-caprolactone, γ-valerolactone, etc., and carbonates may be ethylene carbonate. Alternatively, sulfolanes may be used. Moreover, you may mix and use these.

For example, ethyltrimethylammonium tetrafluoroborate (ETMA ⁺ BF ₄ ⁻ ), which is a quaternary ammonium salt, can be used as the solute. As the solute anion, those containing a fluorine atom are preferable in terms of withstand voltage characteristics, and BF ₄ ⁻ or PF ₆ ⁻ is particularly preferable. The concentration of the solute is preferably in the range of 0.5 to 2.0 mol / l.

The solute is preferably an onium salt, of which a quaternary ammonium salt is preferred, and among them, at least one functional group of four functional groups surrounding the nitrogen atom is different from other functional groups, such as ETMA ^+. A quaternary ammonium salt having a constitution is preferred. Such a quaternary ammonium salt is superior to other quaternary ammonium salts in that it suppresses the electrolyte from creeping up in the electric double layer capacitor.

  In addition, a solvent and a solute are not limited to the said chemical species, If it forms an electric double layer in the positive electrode 2 and the negative electrode 3 in electrolyte solution, it will not be limited.

  And the tertiary amine compound shown to Formula (1) is included in this electrolyte solution. The content of the tertiary amine compound in the electrolytic solution is preferably 0.01 wt% or more and 5 wt% or less. This compound functions as a buffer in the electrolytic solution, and suppresses fluctuations in pH in the electrolytic solution. Therefore, hydrolysis of the solvent caused by a small amount of water contained in the electrolytic solution is suppressed, fluctuations in pH in the electrolytic solution are suppressed, and reliability can be improved.

In the formula (1), R ³ mainly has a straight chain having 3 or more carbon atoms and a hydroxy group bonded to the terminal thereof. The carbon atom constituting R ³ may have hydrogen or an alkyl group in the side chain portion, or may be substituted with a halogen atom or a halogen-substituted alkyl group.

  Moreover, although there exists a possibility that decomposition | disassembly of a solvent may arise with the fluctuation | variation of pH near an electrode, decomposition | disassembly of this solvent can also be suppressed by using a tertiary amine compound in electrolyte solution. Thereby, the fluctuation | variation of the composition ratio of electrolyte solution can be suppressed, and the fall of characteristics, such as a capacity | capacitance and resistance accompanying progress of a charging / discharging cycle, can be suppressed.

  Although the production | generation method of the tertiary amine compound represented by Formula (1) is not specifically limited, As an example, it can produce | generate with the following method. That is, the corresponding alkyl halomethyl ketone and dimethylamine are used as raw materials. These raw materials are reacted in an alcohol solvent such as ethanol. A tertiary amine compound can be produced by such an operation.

  The alcohol to which the raw material is added is, for example, 3 to 50 times the amount of the raw material. As the reaction proceeds, hydrogen halide is generated, and the produced amine compound is a hydrogen halide salt. Therefore, the target amine compound can be obtained by neutralizing the reaction product using an appropriate base. Moreover, it refine | purifies as needed and uses it for electrolyte solution.

(Performance evaluation test)
Hereinafter, effects of the electrolytic solution and the electric double layer capacitor according to the present embodiment will be described using specific examples.

The electrolyte solution of Sample 1 contains γ-butyrolactone as an organic solvent. The ETMA ⁺ BF ₄ is a quaternary ammonium salt as a solute ^- containing. Its concentration is 1.0 mol / l. Further, as an example of the tertiary amine compound, 1.0 wt% of the compound A represented by the formula (2) is included.

  The electrolyte solution of sample 2 is an electrolyte solution having the same configuration as sample 1 except that compound A is not included.

  These samples 1 and 2 are evaluated using the H-type cell shown in FIG. FIG. 2 is a schematic diagram of an H-type cell used in an electrolytic solution performance evaluation test in the embodiment of the present invention. The H-type cell has an H-type glass case 26, a positive electrode 22, a negative electrode 23, and a glass filter 24. The glass case 26 includes a pair of bottomed cylindrical cell portions 26A and a cylindrical relay portion 26B that connects the cell portions 26A. The positive electrode 22 and the negative electrode 23 are formed of Pt foil and are accommodated in the respective cell portions 26A. The glass filter 24 is disposed in the relay part 26B to isolate the positive electrode 22 and the negative electrode 23 from each other. The glass case 26 is filled with the electrolytic solution 28. The positive electrode 22 and the negative electrode 23 are electrically connected to a power source 29.

In a dry room, a direct current is applied to samples 1 and ^{2 at} a current density of 1 mA / cm ² for 60 minutes using the H-type cell shown in FIG. Then, the pH of the electrolyte solution 28 on the negative electrode 23 side is measured from the application start time to the time point of 60 minutes, and the pH on the negative electrode 23 side after the lapse of 20 minutes and 60 minutes is compared in each sample.

  In addition, an electric double layer capacitor using the electrolyte solutions of Samples 1 and 2 is manufactured, and a life test is performed under conditions of 60 ° C., 2.5 V, and 250 hours. Then, the capacity retention rates of the respective electric double layer capacitors after 250 hours are compared.

  The evaluation results are shown in (Table 1). From Table 1, the electrolyte solution of Sample 1 containing Compound A has a lower pH value compared to Sample 2 and has a lower pH value. In addition, it can be seen that the electric double layer capacitor using the electrolytic solution of Sample 1 has suppressed capacity deterioration compared to the electric double layer capacitor using the electrolytic solution of Sample 2.

  As described above, the electrolytic solution of the present embodiment includes the tertiary amine compound represented by the formula (1) as the compound in the electrolytic solution. Thereby, a tertiary amine compound acts on the water | moisture content in electrolyte solution, and suppresses hydrolysis of a solvent. Therefore, it is possible to suppress fluctuations in pH in the electrolytic solution that may occur during repeated charging and discharging of the electric double layer capacitor using the electrolytic solution.

In addition to compound A, it has been confirmed that the same result is obtained when either or both of R ¹ and R ² are ethyl groups.

  In the above description, the tertiary amine compound contained in the electrolytic solution has been intentionally included in the electrolytic solution, but the configuration of the present invention is not limited to this. For example, when a quaternary ammonium salt is used as a solute and γ-butyrolactone is used as a solvent, these react to produce a tertiary amine compound by the following reaction. Thus, even if the tertiary amine compound is formed after the electric double layer capacitor is assembled, the fluctuation in pH is suppressed.

The above reaction formula consists of steps 1-6. In Step 1, a hydroxide ion (OH ⁻ ) generated by electrolyzing water contained in a trace amount in the electrolytic solution attacks a hydrogen atom of a methyl group of an ethyltrimethylammonium cation that is a cation. As a result, this methyl group releases a proton. Therefore, ammonium ylide is produced.

  In Step 2, this ammonium ylide reacts with γ-butyrolactone as a solvent to form one compound. Thereafter, as shown in Step 3, in order to stabilize this compound, a 5-membered ring derived from γ-butyrolactone is opened, and a compound having a carbonyl group shown in Step 4 is formed.

  This compound reacts with moisture contained in the electrolytic solution as shown in Step 5, and finally, as shown in Step 6, Compound A which is a kind of tertiary amine compound having a molecular weight of 145 is generated.

  The compound A produced from this reaction is contained in the electrolyte at a content in the range of 0.01 wt% or more and 5 wt% or less, thereby suppressing the deterioration of the characteristics of the electric double layer capacitor accompanying the charge / discharge cycle. can do.

  The content of the tertiary amine compound in the electrolytic solution depends on the amount of moisture present in the capacitor element 1. The amount of water is the positive electrode 2, the negative electrode 3, the separator 4, and the water that could not be removed from the electrolyte solution in addition to the moisture that could not be removed from the electrolytic solution, and when cycle charge / discharge was performed using an electric double layer capacitor. The moisture generated by decomposing the cellulose component contained in the capacitor element 1 is also included. Moreover, it is preferable as a production | generation condition that it is charged / discharged on 60 degreeC or more as high temperature conditions as charging / discharging environment.

  In the above description, the ethyltrimethylammonium cation is used as the cation forming ammonium ylide, but the present invention is not limited to this. In addition, a dimethyldiethylammonium cation etc. can be used in the quaternary ammonium cation whose substituent is composed of a methyl group or an ethyl group.

  Next, the effect when a tertiary amine compound is produced after the electric double layer capacitor is assembled will be described using a specific example.

Samples 3 to 8 use an electrolytic solution having a concentration of 0.9 mol / l using ETMA ⁺ BF ₄ ⁻ as a solute and γ-butyrolactone as a solvent, except that the amount of moisture in the capacitor element 1 is different. ing. Other than this, an electric double layer capacitor was fabricated in the same manner as Sample 1. Sample 9 has the same configuration as Sample 4 except that tetraethylammonium tetrafluoroborate was used as the solute. A life test is performed on the electric double layer capacitors of Samples 3 to 8. This test was conducted under conditions of 60 ° C., 2.5 V, and 250 hours. The amount of tertiary amine compound produced in each electric double layer capacitor after the test, the pH value of the electrolytic solution, and the capacity retention rate. Are comparing. The results are shown in (Table 2).

  In Samples 3 to 5 in which the content of the tertiary amine compound is 0.01 wt% or more and 5 wt% or less, the change in pH is suppressed and the capacity retention is not significantly reduced. On the other hand, the samples 6 and 7 in which the content of the tertiary amine compound exceeded 5 wt%, the sample 8 in which the content of the tertiary amine compound was less than 0.01 wt%, and the sample 9 having a different cation were capacity retention rates. As the pH decreases, the pH increases and alkalization is promoted.

  Thus, when the moisture content in the capacitor element 1 is within a certain range and the condition that the tertiary amine compound is contained in the electrolytic solution in an amount of 0.01 wt% or more and 5 wt% or less is satisfied, the pH change and the capacity retention rate are reduced. Reduction is suppressed.

  Next, other compounds having the same effect as the tertiary amine compound will be described.

  The electrolytic solution and the electric double layer capacitor using the electrolytic solution may include a quaternary ammonium salt having a cation represented by formula (3) in the electrolytic solution. In this case as well, fluctuations in pH in the electrolytic solution can be suppressed.

(N represents nitrogen, R ^{1 to} R ³ represent organic substituents having 1 or more carbon atoms, and R ^{1 to} R ³ have the same or different composition. R ^α is 1 or more carbon atoms. At least one of the substituents is a hydrogen atom closest carbon atom to the nitrogen atom of the .R ¹ to R ³ and R ^alpha having an electron-withdrawing group to a carbon atom constituting the R ^alpha is attached).

The cation reacts with OH ⁻ in the electrolytic solution that causes the fluctuation of pH, and from this reaction, nitrogen ylide having a nitrogen atom and carbon atom bond represented by the following formula (4) is easily formed. Can be generated. By this reaction, when the electric double layer capacitor repeats charging and discharging, an increase in OH ⁻ in the electrolytic solution is suppressed, and a change in pH in the electrolytic solution to the alkali side is suppressed.

(C represents carbon, N represents nitrogen, and R ^{a to} R ^e represent organic or inorganic substituents).

In the cation, a hydrogen atom is bonded to a carbon atom directly bonded to the nitrogen atom in at least one of the substituents R ^{1 to} R ³ and R ^α existing around the nitrogen atom. In order to exhibit the effect of suppressing the fluctuation in pH, it is necessary to react with OH ⁻ using the cation to generate nitrogen ylide. That is, it is necessary to react protons generated by ionization of the hydrogen atoms with OH ⁻ in the electrolytic solution. That is, in order to facilitate the reaction between protons and OH ⁻ , it is necessary to lower the electron density of the hydrogen atoms to create a state in which the hydrogen atoms can be easily extracted in the cation.

Here, as a method for reducing the electron density, at least one electron withdrawing group is bonded to the carbon of R ^α in the chemical formula (3). By providing the electron-withdrawing group on R ^alpha, lower the electron density of the hydrogen atoms involved in the formation of nitrogen ylide, easily pull out the hydrogen atom. Thereby, it becomes possible to promote reaction with OH ^{− in the} cation.

Note that the electron-withdrawing group, for example _{-F, -Cl, -Br, -OR,} = O, -COR, -CO 2 R, -NO 2, -SO 2 R, -CN, -CR = CR _{2, -C≡R, -CH x F y} , is _-CH v _F w _-CH x F _y and the like. Here,-, =, ≡ represents the bonding state of atoms or molecules, R represents an inorganic or organic substituent, and the rest represent atoms based on the periodic table. Further, v and w are integers of 0 or more and 2 or less and satisfy v + w = 2, and x and y are integers of 0 or more and 3 or less and satisfy x + y = 3. Among _{these, -F, -COR, -NO 2,} -CN , etc. has a high electron-withdrawing, OH ^- can promote the reaction between.

In the formula (3), R ^{1 to} R ³ are organic substituents having 1 or more carbon atoms bonded to the nitrogen atom located at the center. R ^{1 to} R ³ may have a configuration having the electron withdrawing group. In addition, the above-described effect of reducing the electron density may vary depending on the positional relationship between the electron-withdrawing group provided in the cation represented by the formula (3) and the hydrogen atom extracted during ylide generation. However, by having an electron withdrawing group, alkalization is suppressed as compared with a conventional quaternary ammonium salt having no electron withdrawing group. Therefore, when it is intended to promote the ylation of the quaternary ammonium salt, a configuration in which the electron withdrawing group is bonded to a carbon atom having a hydrogen atom to be extracted is preferable.

  However, this nitrogen ylide is generally unstable and it is difficult to produce it stably. One means for solving this is to reduce the electron density of the carbon atom bonded to the nitrogen atom by the electron withdrawing group. This is because the electron density can be widely dispersed in the molecule by reducing the electron density of the carbon atom using the electron withdrawing group. Thereby, decomposition | disassembly of nitrogen ylide is suppressed and nitrogen ylide becomes stable.

By stabilizing the nitrogen ylide in this way, the energy barrier existing in the process of reacting from the quaternary ammonium salt to the nitrogen ylide becomes smaller. Therefore, the reaction to ylide can be promoted. Therefore, OH ⁻ in the electrolytic solution and the quaternary ammonium cation represented by the formula (3) react stably even under high temperature conditions, and the fluctuation of the pH in the capacitor can be suppressed.

  Further, the nitrogen ylide can react with a substance having an appropriate double bond. For example, it reacts with γ-butyrolactone having a carbonyl group, propylene carbonate, etc., and is converted into an electrically neutral substance that does not affect the electrical characteristics.

  In addition, although the production | generation method of the quaternary ammonium salt containing the cation shown in Formula (3) is not specifically limited, The following methods are mentioned as an example.

  First, dimethyl carbonate (9.0 g, 100 mmol), an amine (100 mmol) having an electron-withdrawing group, and methanol as a solvent are placed in an autoclave and reacted at 115 ° C. and 0.5 MPa for 12 hours while stirring. After the reaction, unreacted raw materials and solvent are removed by an evaporator to obtain methyl carbonate of methylated product. This methyl carbonate is dissolved in water and heated under reduced pressure to further remove methanol.

  Next, an aqueous solution of tetrafluoroboric acid is added to the aqueous solution of methyl carbonate so as to be equimolar with the methyl carbonate, and the mixture is heated and stirred. When gas generation ceases, the gas is further removed by heating under reduced pressure. Then, if water is removed by evaporating or the like, an example of a quaternary ammonium salt represented by the formula (3) can be prepared.

In the formula (3), R ^{1 to} R ³ are substituents having 2 or less carbon atoms, and among these four substituents including R ^α surrounding the nitrogen atom, the substitution having 1 carbon atom is performed. A configuration having two or three groups is preferred. A quaternary ammonium salt constituted with such a carbon number relationship is liable to form an ylide. And by providing an electron withdrawing group in such a quaternary ammonium salt, the stabilization of ylide can be improved in addition to the ease of iridation. Thereby, the pH fluctuation in the electric double layer capacitor can be further suppressed. Therefore, in consideration of the positional relationship between the effect of the electron withdrawing group and the hydrogen atom to be extracted, the R ^α preferably has a configuration with 1 carbon atom.

  Next, an example in which a different compound is applied will be described. That is, the electrolytic solution and the electric double layer capacitor using the electrolytic solution may include a quaternary phosphonium salt having a cation represented by formula (5) in the electrolytic solution. In this case as well, fluctuations in pH in the electrolytic solution can be suppressed.

P represents phosphorus, R ^{1 to} R ³ represent organic substituents having 1 or more carbon atoms, and the compositions of R ^{1 to} R ³ are the same or at least one different. The R ^alpha 1 or more carbon atoms, have an electron-withdrawing group to a carbon atom constituting the R ^alpha, at least one of the substituents is the closest carbon atom to the phosphorus atom of R ¹ to R ³ and R ^alpha A hydrogen atom is bonded to. Here, the electron withdrawing group provided in Formula (5) is the same as that in Formula (3).

  In addition, although the production | generation method of this quaternary phosphonium salt is not specifically limited, The following method is mentioned as an example.

  In an inert atmosphere, triphenylphosphine is dissolved in a suitable solvent such as tetrahydrofuran and reacted with alkyl halide to prepare alkyltriphenylphosphine halide. Next, alkyltriphenylphosphine tetrafluoroborate, which is an example of a quaternary phosphonium salt containing a cation represented by formula (5), can be prepared by anion exchange reaction.

In the cation represented by the formula (5), a structure having 2 or 3 substituents having 1 carbon atom among the four substituents including R ^α surrounding the phosphorus atom is preferable. A quaternary phosphonium salt configured in such a relationship with the number of carbons easily forms an ylide, and by providing an electron withdrawing group in such a quaternary phosphonium salt, in addition to the original ylidization ease. Thus, stabilization of ylide can be improved. Thereby, the pH fluctuation in the electric double layer capacitor can be further suppressed. Therefore, in consideration of the positional relationship between the effect of the electron withdrawing group and the hydrogen atom to be extracted, the R ^α preferably has a configuration with 1 carbon atom.

  Next, an example in which a different compound is applied will be described. That is, an electrolytic solution and an electric double layer capacitor using the same include a tertiary sulfonium salt or a tertiary sulfooxonium salt having a cation represented by formula (6) or formula (7) in the electrolytic solution. It may be a configuration. In this case as well, fluctuations in pH in the electrolytic solution can be suppressed.

However, S represents sulfur, O represents oxygen, R ¹ and R ² represent organic substituents having 1 or more carbon atoms, and the compositions of R ¹ and R ² are the same or different . R ^α has 1 or more carbon atoms and has an electron withdrawing group on the carbon atom constituting R ^α . At least one substituent of R ¹ , R ² and R ^α has a hydrogen atom bonded to the carbon atom closest to the sulfur atom of the cation. Here, the electron withdrawing group provided in Formula (6) and Formula (7) is the same as in Formula (3).

  In addition, although the production | generation method of said tertiary sulfonium salt or tertiary sulfooxonium salt is not specifically limited, The following method is mentioned as an example.

  Trialkyloxonium tetrafluoroboric acid is added to an organic sulfur compound dissolved in an appropriate solvent such as tetrahydrofuran in an inert atmosphere, and the mixture is reacted by stirring at room temperature and normal pressure. After the reaction, the corresponding salt can be prepared by removing the solvent and unreacted raw material and drying under reduced pressure.

  As the organic sulfur compound, sulfide is used when preparing a tertiary sulfonium salt, and sulfoxide is used when preparing a tertiary sulfoxonium salt. Alternatively, when aryl sulfide or aryl sulfoxide is used, the corresponding sulfonium salt or sulfooxonium salt can be prepared by reacting in the presence of an appropriate alkyl halide and silver borofluoride.

  Thus, the effect of inhibiting alkalinization can be enhanced by providing an electron-withdrawing group in the substituent of the onium salt.

  In the electrolytic solution of the present invention, pH fluctuation is suppressed. Therefore, in the electric double layer capacitor using this electrolytic solution, the electrolytic solution is prevented from leaking to the outside. Therefore, the electric double layer capacitor in the present invention has high reliability as a power storage device. Therefore, it can be used in electronic equipment applications and in-vehicle applications that require high reliability.

DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Positive electrode 2A, 3A Current collector 2B, 3B Polarization electrode layer 3 Negative electrode 4 Separator 5A, 5B Lead wire 6 Case 7 Sealing member 7A Through-hole 22 Positive electrode 23 Negative electrode 24 Glass filter 26 Glass case 26A Cell part 26B Relay Part 28 Electrolyte 29 Power supply

Claims (2)

A capacitor element having a positive electrode and a negative electrode;
A case containing the capacitor element together with an electrolytic solution;
The electrolyte is
Lactones ,
A quaternary ammonium salt contained in the lactone and a tertiary amine compound represented by the formula (1),
An electric double layer capacitor comprising the tertiary amine compound in an amount of 0.01 wt% to 5 wt% .

C represents a carbon atom, H represents a hydrogen atom, O represents an oxygen atom, and N represents a nitrogen atom. The electric double layer capacitor according to claim 1, wherein the lactone is γ-butyrolactone.

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